The relationship among canine brain temperature, metabolism, and function during hypothermia

Area of Science:

• Neuroscience
• Physiology
• Cardiovascular Surgery

Background:

• Cerebral protection during hypothermia is linked to reduced metabolic activity.
• The precise relationship between brain temperature and cerebral metabolic rate of oxygen consumption (CMRO2) below 28°C remains unclear.

Purpose of the Study:

• To investigate the relationship between brain temperature and CMRO2 in dogs during profound cooling.
• To characterize the temperature coefficient (Q10) for CMRO2 across different hypothermic ranges.

Main Methods:

• Eight dogs were cooled from 37°C to 14°C under cardiopulmonary bypass.
• Cerebral metabolic rate of oxygen consumption (CMRO2) and electroencephalogram (EEG) were monitored at various temperatures.
• The temperature coefficient (Q10) for CMRO2 was calculated for different temperature intervals.

Main Results:

• The Q10 for CMRO2 between 37°C and 27°C was 2.23.
• Between 27°C and 14°C, the mean Q10 doubled to 4.53, indicating accelerated metabolic suppression.
• EEG showed burst suppression at or below 22°C, with continued activity at 14°C in most dogs.

Conclusions:

• CMRO2 decreases more steeply with temperature below 27°C than previously characterized.
• Profound hypothermia significantly enhances cerebral metabolic suppression.
• EEG activity persists even at 14°C, suggesting continued neuronal function under deep hypothermia.